Colure, in astronomy, is either of the two principal meridians of the celestial sphere.^[1] The term is now rarely used and may be considered obsolete.

The equinoctial colure is the meridian or great circle of the celestial sphere which passes through the celestial poles and the two equinoxes:^[1] the first point of Aries and the first point of Libra. It is the great circle consisting of all points on the celestial sphere with Right Ascension equal to 0 hours or 12 hours (equivalent to RA 0° / 180°).

The equinoctial colure passes through the following constellations:

The solstitial colure is the meridian or great circle of the celestial sphere which passes through the poles and the two solstices:^[1] the first point of Cancer and the first point of Capricorn. It is the great circle consisting of all points on the celestial sphere with Right Ascension equal to 6 hours or 18 hours (equivalent to RA 90° / 270°).

The solstitial colure passes through the following constellations:

• Celestial coordinate system
• Ecliptic
• Celestial sphere
• Right ascension
• Equinox
• Solstice

•  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Colure". Encyclopædia Britannica. Vol. 6 (11th ed.). Cambridge University Press. p. 748.
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